The human circulatory system is a two-part system and its purpose is to bring oxygen-bearing blood to all tissues of the body. When a heart contracts, it pushes the blood out into two major loops or cycles. In the systemic loop, the blood circulates into the body's cardiovascular system, bringing oxygen to all the organs, structures, and tissues, and collecting carbon dioxide waste. In the pulmonary loop, the blood circulates to and from the lungs to exchange carbon dioxide for oxygen. The systemic cycle is controlled by the left side of the heart and the pulmonary cycle by the right side of the heart.
The systemic loop begins when the oxygen-rich blood coming from the lungs enters the left atrium of the heart. As the left atrium fills, it presses open the mitral valve and the blood flows down into the left ventricle. When the ventricles contract during, a heartbeat, the blood in the left ventricle is forced into the aorta. The blood leaving the aorta brings oxygen to all the body's cells through a network of smaller arteries and capillaries.
The oxygen-depleted blood from the body returns to the heart through a network of veins. All of the blood from the body is eventually collected into the two largest veins: the superior vena cava, which collects blood from the upper body, and the inferior vena cava, which collects blood from the lower body. Both the vena cava empty the blood into the right atrium of the heart. From here the blood begins its journey through the pulmonary cycle.
From the right atrium, the blood descends into the right ventricle through the tricuspid valve. When the right ventricle contracts, the blood is pushed through the pulmonary valve into the pulmonary artery that branches into two main parts: one going to the left lung, one to the right lung. The fresh, oxygen-rich blood returns to the left atrium of the heart through the pulmonary veins.
Although the circulatory system is made up of two cycles, both the cycles take place at the same time. The contraction of the heart muscle starts in the two atria, which push the blood into the two ventricles. Then the walls of the ventricles compress and force the blood out into the two arteries: the aorta to the body and the pulmonary artery to the lungs. Afterwards, the heart muscle, relaxes, allowing blood to flow in from the veins and fill the atria again.
Congestive heart failure (CHF) is a condition affecting millions of people worldwide. CHF results from a weakening or stiffening of the heart muscle that commonly is caused by myocardial ischemia (due to, e.g., myocardial infarction) or cardiomyopathy (e.g., rnyocarditis, amyloidosis). CHF causes reduced cardiac output and inadequate blood to meet the needs of body tissues. CHF is generally classified into systolic heart failures (SHF) or diastolic heart failures (DHF).
In a SHF, the pumping action of a heart is reduced or weakened. A normal ejection fraction (EF), which is a function of the volume of blood ejected out of the left ventricle (stroke volume) divided by the maximum volume remaining in the left ventricle at the end of the diastole or relaxation phase, is greater than 50%. In a systolic heart failure, EF is decreased to less than 50%. A patient with SHF may have an enlarged left ventricle because of cardiac remodeling developed to maintain an adequate stroke-volume. This pathophysiological phenomenon is often associated with increased atrial pressure and left ventricular filling pressure.
DHF is a heart failure refers to a decline in the performance of one of or both the ventricles of the heart during a diastole. Generally, DHF is a failure of the ventricle to adequately relax and expand, resulting in a decrease in the stroke volume of the heart. Thus, DHF is characterized by elevated diastolic pressure in the left ventricle, despite essentially normal/physiologic end diastolic volume (EDV). In a DHF patient, the stiffness of the left ventricular makes it more difficult for blood to enter it from the left atrium. As a result, pressure rises in the atrium and is transmitted back to the pulmonary venous system, thereby increasing its hydrostatic pressure and promoting pulmonary edema. DHF afflicts between 30% and 70% of those patients with CHF.
Presently, there are very few treatment options for patients suffering from DHF. Treatments for CHF include: (1) pharmacological treatments, (2) assisting systems, and (3) surgical treatments. Pharmacological treatments, e.g., with diuretics, are used to reduce the workload of as heart by reducing blood volume and preload. While drug treatment improves quality of life, it has little effect on survival. Assisting devices, e.g., mechanical pumps, are used to reduce the load on the heart by performing all or part of the pumping function normally done by the heart. However, in a chronic ischemic heart, a high-rate pacing may lead to increased diastolic pressure, calcium overload, and damage to the muscle fibers. There are at least three surgical procedures for treatment of a heart failure: (1) heart transplant. (2) dynamic cardiomyoplasty, and (3) the Batista partial left ventriculectomy. These surgical treatments are invasive and have many limitations.
There are several known techniques that can be used to treat various symptoms of DHF. Without attempting to characterize the following references, for example, U.S. Pat. No. 8,091,556 by Keren et al. discloses the use of an interatrial pressure relief shunt with a valve and a tissue affixation element at each end of the shunt; U.S. Pat. No. 8,043,360 by McNamara et al. discloses the use of an interatrial pressure vent to allow sufficient flow from the left atrium to the right atrium to relieve an elevated left atrial pressure and resulting patient symptoms; and United States Patent Application Publication No. 20050165344 by Dobak discloses a pressure relief system with an interatrial septal conduit and an emboli barrier or trap mechanism to prevent thrombi or emboli from crossing the conduit into the left sided circulation and causing cryptogenic strokes. Dobak also discloses a conduit with a one-way valve which directs blood flow from the left atrium to the right atrium.
The constantly evolving nature of heart failure represents a significant challenge for the treatment. Therefore, there is a need for novel and adaptable methods and devices for treating DHF, for example, by reducing the flow and/or the pressure in the pulmonary circulation system, and the pressure in the left atrium.